Designed onFaculty of Electrical Engineering and Informatics

Department of Electronics and Multimedia communications

Technical University of Kosice2007

Semestral project

EVAL-AD9952-kemt07

Evaluation board for DDS frequency synthesizerfrom ANALOG DEVICES, INC.

FEATURESBoard includes DDS synthesizer, wideband differential amplifier, wideband transformer and LPF 150MHz for generating frequencies up to 150 MHzSupply 3.3V with onboard voltage regulator 1.8VConnectors for control of synthesizer functions from controllerTypical consuming 3.3V 90mAOutput 0dBm up to 120 MHz

GENERAL DESCRIPTIONThis board is designed to allow students to evaluate the performance of AD9952 Digital Direct Synthesizer. It contains the AD9952 DDS,crystal 20MHz, wideband differential amplifier THS4520, wideband transformer WB2-1-2, Low pass filter 150MHz, SMA connectors for output, connector for control of DDS from controller,power connectors and voltage regulator 1.8V TL3021 [3]

EVAL-AD9952-kemt07

Figure 1. Block diagram of EVAL board

THEORY OF OPERATION

DDS DESCRIPTION

The AD9952 [1] is fully integrated direct digital synthesis (DDS) chip featuring a 14 - bit DAC and operating up to 400 MSPS it is capable of generating a frequencies up to 200MHz. The AD9952 is designed to provide fast frequency hopping and fine tuning resolution (32 - bit frequency tuning word). All control words are loaded into the AD9952 via a serial I/O port.The internal circuits of the AD9952 consist of the following main sections (Fig.2): a buffered oscillator input, PLL multiplier, frequency and phase modulators, COS ROM, a digital -to- analog converter, a fast comparator and I/O buffer.

Figure 2. Functional block diagram for AD9952

EVAL-AD9952-kemt07

THEORY OF OPERATIONSine waves are typically thought of in terms of their magnitude form a(t) = sin(t). These harmonics signals are nonlinear but the angular information is linear function of time. The DDS method uses a phase accumulator, driven by the specified frequency, which accumulates the phase increments. The phase is incremented by each driving frequency clock tick. The size of the phase increment determines the actual output frequency. The binary width of the phase accumulator (accumulator overflows) determines the minimum frequency, which is equal to the frequency step, achievable by the DDS. The minimum frequency is defined by

and therefore the output frequency is

where F is a tuning number and n is the accumulator width in bits.Since phase information maps directly into amplitude, the COS ROM uses digital phase information as an address to look-up a table and converts the phase information into amplitude. This amplitude words are converted in fast digital -to- analog converter into current source. The AD9952 have differential current source output and maximal current is possible to adjust with DAC RSET value.

DIFFERENTIAL AMPLIFIER DESCRIPTION

The THS4520 [4] is wideband, fully differential amplifier with Rail to Rail output. It is optimized for 5V and 3.3V single supply systems. In this project was used positive feedback [7]. The positive feedback makes the value of the output resistor appear larger than what it actually is when viewed from the line. Still, the voltage dropped across the resistor depends on its actual value, resulting in increased efficiency. With standard termination, 36 mW of power is dissipated in the output resistors, as opposed to 13 mW with active termination. That is, 64% less power is wasted with the active termination.

TRANSFORMER DESCRIPTION

The WB2-1-2WSL [6] is wideband transformer with impedance ratio 1:2. In this project was used on transformed output impedance (25Ω) from amplifier to 50Ω for low pass filter. Also for conversion of balanced signals to unbalanced one.

Figure 3. Typical frequency response

EVAL-AD9952-kemt07

LOW PASS FILTER DESCRIPTION

The Low pass filter P7LP-157 [5] used in this project eliminated harmonics product from signal. This filter is 7 th

order elliptical alignments and it frequency response is on Fig.4

Figure 4. Measured insertion loss

EVAL-AD9952-kemt07

Hardware descriptionFor connecting controller and supplying with evaluation board required the female connectors FL10EC for supply and FL20EC for controller. Both connectors have to be with flat cable AWG28-10G and AWG28-20G.The silk screen and the cable diagram for evaluation board are shown above. The board schematic is shown on pages 11.

EVAL-AD9952-kemt07

Figure 5.EVAL - Component side view - Silkscreen

Figure 6. Cable diagram

MEASURED PERFORMANCE OF THE EVAL-AD9952-kemt07These data were measured with RF milivoltmeter BM495A. Output was terminated with 50 ohm.Output power for low frequencies is around 13dBm and slowly decreases to 0 dBm at 120 MHz

Figure 7. Measurements show output voltage

EVAL-AD9952-kemt07

EXAMPLE OF APPLICATION

This EVAL-BOARD was used on application for simple AM/FM transmitter. For the conversion of signal from microphone to digital signal and transforming this signal on frequency word or amplitude word was used controller.The signal was received with correct antena at radius few tens meters.

Principles for transmitting signal for other band like up to 150 MHz is shown on Fig.9. Modulated signal goes to up-convert mixer and is translated around local oscillator frequencies. After this operation the signal is filtered in LPF or HPF and is amplified.

EVAL-AD9952-kemt07

Figure 8. Block diagram - Simple AM/FM transmitter

Figure 9. Block diagram - Transmitter for other frequency band

KNOWN PROBLEMS

For this project was chosen dual layer PCB board with photo sensitivity film. Schema and board was drawing in EAGLE Light software.The soldering parts on board were made with hands. It is necessary to have not shivery hands. The placing and soldering of amplifier seemed to be difficult but it is possible. This package is only 3 mm width and has four pins at every side.The peak around 8MHz (Fig.7) is caused probably by parasitic capacity loop or maybe by bad placement of parts around OpAmp chip. The power decreasing is caused by insertion loss on transformer and on filter. The influence must be inspect on OpAmp. Thermal pad was soldering from bottom side via AgCu wire. Low melting-point alloys were used for soldering.

EVAL-AD9952-kemt07

Figure 10. The detail of hand made soldering amplifier

Example for software controlThis source code is for ATmega8 [2] controller, including SPI interface and many pins necessary for full control function AD9952. This simple code shows the sending of address and data words from controller to DDS chip.

EVAL-AD9952-kemt07

EVAL-AD9952-kemt07

EVALUATION BOARD LAYOUT

Figure 11. EVAL – TOP Layer

Figure 12. EVAL – BOTTOM Layer – As view on bottom side

EVAL-AD9952-kemt07

References

Main Parts Manufacturer Vendor Links[1] AD9952YSVZ Analog Devices, Inc. Dialogue s.r.o http://www.analog.com/UploadedFile

s/Data_Sheets/AD9952.pdf

[2] ATmega8-16 ATMEL S.O.S electronics http://www.atmel.com/dyn/resources/prod_documents/doc2486.pdf

[3] LT3021ES8 Linear Technology S.O.S electronics http://www.linear.com/pc/download

[4] THS4520RGTT Texas Instruments http://www.ti.com/lit/gpn/ths4520

[5] P7LP-157 Coilcraft, Inc. http://www.coilcraft.com/pdfs/lcfilt.pdf

[6] WB2-1-2WSL Coilcraft, Inc. http://www.coilcraft.com/pdfs/wb.pdf

[7] Fully-differential Amplifiers, Texas Instruments SLOA054A

Acknowledgments

This project would not have been possible without the support of many manufacturers who have provided samples parts for the development.

I would like to gratefully acknowledge the following organizations : Analog Devices, Inc. for sample AD9952, Texas Instruments for sample THS4520, Linear Technology for sample LT3021 and

CoilCraft, Inc. for sample the filter and transformer. The acknowledgment belong them for contribution development and educations.

I would like to express my sincere thanks and appreciation to my advisor, Assoc. Prof. Milos Drutarovsky, for guidance and technical discussions, and for providing me with excellent facilities to

pursue my work .

EVAL-AD9952-kemt07

Table 1. Bill of materials for the EVAL-AD9952-kemt07

Item Quantity Reference Description

1 8 C2 C5 C8 C9 C10 C11 C12 C14

1nF ceramic Capacitor 0805

2 4 C3 C6 C13 C19 100nF ceramic Capacitor 0805

3 2 C15 C 16 39pF ceramic Capacitor 0805

4 3 C1 C4 C7 10uF tantal Capacitor SMC_B

5 1 C18 1uF tantal Capacitor SMC_B

6 1 C17 220nF ceramic Capacitor 0805

7 6 FB2 FB3 FB4 FB5 FB6 FB7 Ferrite Beam 1206

8 1 FB1 Ferrite Beam 10mm

9 1 X1 SMA PCBW Female Connector

10 1 Q1 20MHz HC49 Crystal

11 1 TR1 WB2-1-2SLB Transformer CoilCraft

12 1 IC1 LT3021 SOIC8 Voltage Regulator Linear Technology

13 1 IC2 THS4520 QFN16 Differential Amplifier Texas Instruments

14 1 IC3 AD9952 TQFP48 DDS Analog Devices Inc.

15 1 LPF P7LP LPF CoilCraft

16 1 JP1 LPH10RA Connector

17 1 JP2 LPH20RA Connector

18 3 R14 R15 R16 0R0 Resistor Optional 1206

19 2 R4 R18 746Ω Resistor 1206

20 2 R5 R13 560Ω Resistor 1206

21 2 R6 R7 50Ω Resistor 1206

22 2 R8 R11 3.3Ω Resistor 1206

23 1 R1 10k Ω Resistor 1206

24 1 R2 12kΩ Resistor 1206

25 1 R3 68kΩ Resistor 1206

26 1 R12 3.9kΩ Resistor 1206

27 1 R17 1kΩ Resistor 1206

28 1 PCB board Double-sided PCB Made of FR-4 2oz. Copper

EVAL-AD9952-kemt07

EVAL-AD9952-kemt07

Design, production and testing:

B.Sc. Peter PsotaSOU PaT,SNP104KosiceSlovak Republic

Coordinator:

Assoc. Prof. Milos Drutarovsky, Ph.D.Technical University of KosiceDepartment of Electronics & Multimedia CommunicationsPark Komenskeho 13, 041 20 KosiceSlovak Republic